[gnome-shell] scroll-view-fade: Do the offset math in the shader

[Jasper St. Pierre <jstpierre src gnome org>]

commit 5c439f4e9ca040dc16899e50a3cb3b6172cb9b83
Author: Jasper St. Pierre <jstpierre mecheye net>
Date:   Wed Nov 28 16:51:42 2012 -0500

    scroll-view-fade: Do the offset math in the shader
    
    This doesn't (or shouldn't) change the visual appearance of the fade
    effect, but does do all the testing math inside the shader, rather
    than on the CPU. This will make fading the offset much easier in
    the future.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=689249

 src/st/st-scroll-view-fade.c    |   76 ++++++++++++++++----------------------
 src/st/st-scroll-view-fade.glsl |   25 ++++++-------
 2 files changed, 44 insertions(+), 57 deletions(-)
---
diff --git a/src/st/st-scroll-view-fade.c b/src/st/st-scroll-view-fade.c
index 5093e7d..1a9ff1d 100644
--- a/src/st/st-scroll-view-fade.c
+++ b/src/st/st-scroll-view-fade.c
@@ -53,10 +53,10 @@ struct _StScrollViewFade
   gint height_uniform;
   gint width_uniform;
   gint fade_area_uniform;
-  gint offset_top_uniform;
-  gint offset_bottom_uniform;
-  gint offset_left_uniform;
-  gint offset_right_uniform;
+  gint vfade_offset_uniform;
+  gint hfade_offset_uniform;
+  gint vvalue_uniform;
+  gint hvalue_uniform;
 
   StAdjustment *vadjustment;
   StAdjustment *hadjustment;
@@ -121,14 +121,14 @@ st_scroll_view_fade_pre_paint (ClutterEffect *effect)
         cogl_program_get_uniform_location (self->program, "width");
       self->fade_area_uniform =
         cogl_program_get_uniform_location (self->program, "fade_area");
-      self->offset_top_uniform =
-        cogl_program_get_uniform_location (self->program, "offset_top");
-      self->offset_bottom_uniform =
-        cogl_program_get_uniform_location (self->program, "offset_bottom");
-      self->offset_left_uniform =
-        cogl_program_get_uniform_location (self->program, "offset_left");
-      self->offset_right_uniform =
-        cogl_program_get_uniform_location (self->program, "offset_right");
+      self->vfade_offset_uniform =
+        cogl_program_get_uniform_location (self->program, "vfade_offset");
+      self->hfade_offset_uniform =
+        cogl_program_get_uniform_location (self->program, "hfade_offset");
+      self->vvalue_uniform =
+        cogl_program_get_uniform_location (self->program, "vvalue");
+      self->hvalue_uniform =
+        cogl_program_get_uniform_location (self->program, "hvalue");
     }
 
   parent_class = CLUTTER_EFFECT_CLASS (st_scroll_view_fade_parent_class);
@@ -207,38 +207,24 @@ st_scroll_view_fade_paint_target (ClutterOffscreenEffect *effect)
   if (h_scroll_visible)
       fade_area[1][1] -= clutter_actor_get_height (hscroll);
 
-  st_adjustment_get_values (self->vadjustment, &value, &lower, &upper, NULL, NULL, &page_size);
+  if (self->vvalue_uniform > -1)
+    {
+      st_adjustment_get_values (self->vadjustment, &value, &lower, &upper, NULL, NULL, &page_size);
+      value = (value - lower) / (upper - page_size - lower);
+      cogl_program_set_uniform_1f (self->program, self->vvalue_uniform, value);
+    }
 
-  if (self->offset_top_uniform > -1) {
-    if (value > lower + 0.1)
-      cogl_program_set_uniform_1f (self->program, self->offset_top_uniform, self->vfade_offset);
-    else
-      cogl_program_set_uniform_1f (self->program, self->offset_top_uniform, 0.0f);
-  }
-
-  if (self->offset_bottom_uniform > -1) {
-    if (value < upper - page_size - 0.1)
-      cogl_program_set_uniform_1f (self->program, self->offset_bottom_uniform, self->vfade_offset);
-    else
-      cogl_program_set_uniform_1f (self->program, self->offset_bottom_uniform, 0.0f);
-  }
-
-  st_adjustment_get_values (self->hadjustment, &value, &lower, &upper, NULL, NULL, &page_size);
-
-  if (self->offset_left_uniform > -1) {
-    if (value > lower + 0.1)
-      cogl_program_set_uniform_1f (self->program, self->offset_left_uniform, self->hfade_offset);
-    else
-      cogl_program_set_uniform_1f (self->program, self->offset_left_uniform, 0.0f);
-  }
-
-  if (self->offset_right_uniform > -1) {
-    if (value < upper - page_size - 0.1)
-      cogl_program_set_uniform_1f (self->program, self->offset_right_uniform, self->hfade_offset);
-    else
-      cogl_program_set_uniform_1f (self->program, self->offset_right_uniform, 0.0f);
-  }
+  if (self->hvalue_uniform > -1)
+    {
+      st_adjustment_get_values (self->hadjustment, &value, &lower, &upper, NULL, NULL, &page_size);
+      value = (value - lower) / (upper - page_size - lower);
+      cogl_program_set_uniform_1f (self->program, self->hvalue_uniform, value);
+    }
 
+  if (self->vfade_offset_uniform > -1)
+    cogl_program_set_uniform_1f (self->program, self->vfade_offset_uniform, self->vfade_offset);
+  if (self->hfade_offset_uniform > -1)
+    cogl_program_set_uniform_1f (self->program, self->hfade_offset_uniform, self->hfade_offset);
   if (self->tex_uniform > -1)
     cogl_program_set_uniform_1i (self->program, self->tex_uniform, 0);
   if (self->height_uniform > -1)
@@ -517,8 +503,10 @@ st_scroll_view_fade_init (StScrollViewFade *self)
   self->height_uniform = -1;
   self->width_uniform = -1;
   self->fade_area_uniform = -1;
-  self->offset_top_uniform = -1;
-  self->offset_bottom_uniform = -1;
+  self->vfade_offset_uniform = -1;
+  self->hfade_offset_uniform = -1;
+  self->vvalue_uniform = -1;
+  self->hvalue_uniform = -1;
   self->vfade_offset = DEFAULT_FADE_OFFSET;
   self->hfade_offset = DEFAULT_FADE_OFFSET;
 
diff --git a/src/st/st-scroll-view-fade.glsl b/src/st/st-scroll-view-fade.glsl
index 4b07642..7897c7b 100644
--- a/src/st/st-scroll-view-fade.glsl
+++ b/src/st/st-scroll-view-fade.glsl
@@ -22,10 +22,10 @@
 uniform sampler2D tex;
 uniform float height;
 uniform float width;
-uniform float offset_bottom;
-uniform float offset_top;
-uniform float offset_right;
-uniform float offset_left;
+uniform float vfade_offset;
+uniform float hfade_offset;
+uniform float vvalue;
+uniform float hvalue;
 
 /*
  * Used to pass the fade area to the shader
@@ -50,17 +50,16 @@ void main ()
         return;
 
     float ratio = 1.0;
-    float fade_bottom_start = fade_area[1][1] - offset_bottom;
-    float fade_right_start = fade_area[1][0] - offset_right;
-    float ratio_top = y / offset_top;
+    float fade_bottom_start = fade_area[1][1] - vfade_offset;
+    float fade_right_start = fade_area[1][0] - hfade_offset;
+    float ratio_top = y / vfade_offset;
     float ratio_bottom = (fade_area[1][1] - y)/(fade_area[1][1] - fade_bottom_start);
-    float ratio_left = x / offset_left;
+    float ratio_left = x / hfade_offset;
     float ratio_right = (fade_area[1][0] - x)/(fade_area[1][0] - fade_right_start);
-    bool in_scroll_area = fade_area[0][0] <= x && fade_area[1][0] >= x;
-    bool fade_top = y < offset_top;
-    bool fade_bottom = y > fade_bottom_start;
-    bool fade_left = x < offset_left;
-    bool fade_right = x > fade_right_start;
+    bool fade_top = y < vfade_offset && vvalue > 0;
+    bool fade_bottom = y > fade_bottom_start && vvalue < 1;
+    bool fade_left = x < hfade_offset && hvalue > 0;
+    bool fade_right = x > fade_right_start && hvalue < 1;
 
     if (fade_top) {
         ratio *= ratio_top;